1. Field of the Invention
The present invention relates to an improvement in reducing the value of air resistance of a golf club.
2. Description of Related Art
Hitherto, a golf club and, more particularly, a so-called wood club, has been used in order to drive a golf ball farther. Therefore, it has been necessary to reduce the value of air resistance so as to raise the head speed of the golf club when the golf club is swung.
As shown in FIGS. 32 and 33, which illustrate the results of a wind tunnel test to which an ordinary golf club has been subjected, an air flow passing in a direction from the face of the head toward the back portion is expressed as small dots denoting small resistance and as various arrows in the portions around the head and in the back portion.
This represents a laminar boundary layer which is generated around the head in a direction from the face of the head to the back portion of the same. Furthermore, the air flow is separated from the surface of the head at the rear end portion of the above-described laminar boundary layer, causing a negative pressure region to be formed behind the head. In consequence, an undesirable eddy current is generated around the head. In the above-described state, air in front of the head is compressed and its pressure is thereby raised. On the other hand, air pressure behind the head is reduced, causing a pressure difference to be generated across the head. Therefore, as is well known, drag, which will reduce the head speed, will be generated.
Furthermore, if a boundary layer, referred to as a "turbulent boundary layer", is formed on the surface of the head, the air flow cannot easily be separated from the surface of the head, causing the negative pressure portion behind the head to be reduced. Therefore, as is well known, the drag, which will reduce the head speed, can be reduced.
Although a phenomenon similar to the above-described fact is also generated in the shaft portion of the golf club, the head and the shaft have different Reynolds numbers and the mechanisms which will generate the drag are different since the head and the shaft have different sizes.
Inventions found depending upon the above-described phenomenon have been disclosed in Japanese Laid-Open Patent Publication No. 62-176469 and Japanese Utility Model Laid-Open Publication No. 58-70266.
The above-described conventional golf clubs have been arranged as follows:
For example, according to Japanese Laid-Open Patent Publication No. 62-176469, there has been disclosed a head of a golf club arranged in such a manner that surface treatment for forming a turbulent boundary layer is applied to substantially the entire surface of the head from a portion in the vicinity of the face thereof to the rear side of the same. Another golf club has been known which has been, as shown in FIG. 27, arranged in such a manner that a multiplicity of thin grooves are formed in the surface of the head. Furthermore, there has been a golf club as shown in FIG. 28 and arranged in such a manner that grooves are formed in the entire surface of the head in such a manner that the grooves extend substantially parallel to the face of the head.
In addition, a golf club has been known which is arranged in such a manner that the entire surface of the head is formed in a pile surface as shown in FIG. 29.
As for the shaft of a golf club, there has been disclosed a golf club in Japanese Utility Model Laid-Open Publication No. 58-70266. According to this disclosure, the golf club having a head and a grip comprises a shaft which has linear projections formed in at least its surface near the head, the linear projections being capable of changing a laminar boundary layer of an air flow, which passes along the surface of the head when it is swung, into a turbulent boundary layer. In addition, a shaft as shown in FIG. 30 has been known which is arranged in such a manner that the linear projections to be formed on the surface of the shaft are disposed near the laminar separation point. Furthermore, a shaft as shown in FIG. 31 has been known which is arranged in such a manner that the linear projections to be formed on the surface of the shaft are disposed at positions which make an angle of 60.degree. to 70.degree. from the center line of an air flow which passes along the above-described surface.
However, any of the above-described structures involve a disadvantage in that air resistance reduction of the overall body of the golf club including the head, the hosel and the shaft has not been taken into consideration because all of the arrangements have been employed to reduce the value of air resistance of only the head or the shaft.
That is, it takes too long a time to form grooves in the surface of the overall body of the head in the arrangement shown in FIG. 27, in which a multiplicity of the thin grooves are formed in the entire surface of the head. The same is true of the arrangement as shown in FIG. 28, in which the grooves are formed in the entire surface of the head in such a manner that the grooves extend substantially parallel to the face of the head. In a structure such as that shown in FIG. 29, in which the pile is formed on the entire surface of the head, a problem arises in that the pile will be separated when it is used. In a shaft having the linear projection, tripping wires forming the linear projections must be wound around the surface of the shaft. Therefore, it takes to long a time to fasten the wires, since the wires must be fastened straight with respect to the axis of the shaft at the time of manufacturing the shaft.
Furthermore, an increase in the drag, due to the generation of an eddy current, the rotational direction of which is in substantially the same as the swinging direction, has not been taken into consideration. Therefore, the value of air resistance cannot satisfactorily be reduced.
Furthermore, the conventional golf clubs have not been arranged to meet a necessity which arises in that the state of the surface treatment for reducing the value of air resistance must be different for different golfers, since the head speeds of golf clubs used by the different golfers are different from one another. Therefore, the air resistance generated when the golf club is swung cannot be reduced as desired.